Growls in a lean
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An inexperienced eye might not catch the cupping...I'll bet that's the problem. A wheel bearing would probably growl all the time if it were bad. But, OP...your job is done...you gave the info to your buddy, if he wants to believe, great. If not, great!
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#8
What year, may be the rubber mounts between the swingarm and the frame. The rubber mount is behind the football shaped plate low and aft on the frame. There are 2 bolts clamping the plate to the frame and a center chrome plug to access the swingarm pivot bolt. Basically when the rubbers get worn the swingarm wobbles and when the swingarm wobbles you are throwing the vehicle alignment out. Maybe the growl is the final drive belt cogs rubbing aginst 1 side or the other of the rear pulley. I broke 1 of the plate bolts once pulling holeshots and wheelstands with the wife on the back. Start with the plate, check the bolts, then look at the rubbers.
#10
Look far right to see the plate i am talking about. if you zoom in you will see that I replaced the original grade 5 bolts with grade 8 after fishing that 1st broken bolt out of my frame. This is a 2003 and I replaced my rubbers at around 30K mi in 2009 so it was only 6 years old at that time.